This invention is concerned with a novel process for preparing crosslinked vinyl ester-maleic derivative heteropolymers and derivatives thereof, particularly crosslinked vinyl acetate-maleic anhydried heteropolymers for use as gellants, thickeners and additives for aqueous formulations. In addition, this invention is also concerned with crosslinked heteropolymers prepared by this process.
In the past, crosslinked co-polymers of vinyl esters such as vinyl acetate, and maleic derivatives, such as maleic anhydride, maleic acid, maleic acid esters and maleic acid salts have been described which contain molar ratios of combined vinyl ester to maleic derivative of 1:1 to about 10:1. These polymers have found limited utility in a variety of applications including soil-treatment additives, drilling fluid additives, adhesives and dispersion aids. Generally, these copolymers have been produced by conventional polymerization techniques such as mass, solution, or emulsion polymerization. When aqueous solutions are prepared utilizing copolymers of these conventional processes, the solutions are generally cloudy and exhibit low viscosities and poor viscosity stabilities.
The instant invention is primarily concerned with novel crosslinked maleic anhydride-vinyl acetate heteropolymers which are excellent gellants for aqueous systems and with novel processes for preparing them. In contrast to the prior art these novel crosslinked heteropolymers when incorporated into aqueous systems impart high viscosity with excellent viscosity stability. In addition, many form clear gels which are highly desirable in formulations such as cosmetics.